The objective of this Physician Scientist Award is to provide training and experience in studies of intestinal transport. The specific research topic is to define the mechanisms by which colonic epithelial cells adapt to the changes in intracellular pH and volume that occur as a consequence of exposure to short chain fatty acids (SCFAs). SCFAs are the major source of metabolic energy for colonocytes and are the major anion in the colonic lumen, with concentrations greater than 100mM. It has been shown that the SCFAs have significant effects on the cell volume and pH of various non- colonic cells, but the mechanism of action of SCFAs has not been examined extensively in the colon, which is the only tissue that is exposed to physiologic concentrations of SCFAs greater than 1 mM. The research will be accomplished in two stages. Phase I involves didactic training, training in laboratory and optical techniques, and preliminary data gathering. First, a human colon carcinoma cell line (HT29/C1), which has been demonstrated to be a model of a colonic ion-transporting epithelial cell, will be used to study the mechanisms of SCFA transport, and to define the mechanisms by which other membrane transporters are affected by cellular exposure to SCFAs. The ability of chronic SCFA exposure to regulate these transporters will also be investigated. Phase II will be an intensive research experience to obtain further research experience and to gather preliminary data needed to pursue an independent research career. This second stage involves the use of isolated colonic epithelial cells obtained from rabbit and rat. Using techniques and strategies developed during the study of the HT29/C1 tissue culture model, experiments using native tissue will first examine whether the responses observed in the cell culture model parallel those seen in native epithelia. These studies will be performed using a microscope-based digital imaging system. Experiments will also evaluate the heterogeneity among the different cell types between the colonic crypt epithelial cells and the colonic surface cells, as well as the differences between various colonic cell types. The use of a human tissue culture system allows us to ask questions which cannot be easily addressed in native tissue, while the native tissue studies may more accurately reflect the physiologic events that occur in the human colon.